Naval Observatory in
Wa sh i ng ton, D.C.
As telegraphs encircled the
globe, it became possible to
transmit time signals. In 1833,
the Greenwich Observatory
installed a bright red “time
ball” mounted to a mast on
the observatory roof. The ball
dropped at precisely 1 p.m.
every day, allowing ships on
the River Thames to set their
chronometers in reference to
the observatory clock. By
1850, Astronomer Royal Sir
George Airy was interested in
“electrifying” time. Airy felt it
was a national duty to provide
Greenwich time to the nation.
Daily time signals were being
sent across England by the
1870s.
In America, astronomers
also began to distribute time.
The U.S. Naval Observatory
sent occasional time signals as
early as 1865. By 1869, the
Allegheny Observatory near
Pittsburgh began a time ser-
vice for an area spanning New
York, Chicago, and beyond.
The signal was sent to rail-
roads and jewelry stores.
Jewelers placed connected
clocks in their windows where
customers could set their
watches. Allegheny and other
observatories charged fees to
distribute these time services,
allowing them to fund impor-
tant astronomical research.
Time really was money.
By the late 19th century,
the situation had taken on
international dimensions. In
October 1884, delegates from
around the world gathered
in Washington, D.C., at
the International Meridian
Conference. The goal was to
determine “a common zero of
longitude.” Each of the 24
world time zones would be
reckoned from one prime
meridian and standardized to
mean solar time. Thus,
the beloved sun-
dial was
relegated to gardens and
church cemeteries.
The meridian of the
Greenwich Observatory
was chosen as the zero
point for the world’s time
zones. The decision was
made in part because of
Greenwich’s historical
association with time-
keeping, and the fact that
the United Kingdom still
dominated maritime
commerce. Not all of the
35 delegates were happy.
In particular, the French
insisted the prime merid-
ian not be tied to any one
nation and should be
neutral. French clocks
continued to use time
issued from the Paris
Observatory. They remained
9 minutes and 21 seconds
ahead of Greenwich Mean
Time (GMT) until March 10,- Apparently, even time
can be political.
Astronomers thrive on pre-
cision, and calendar dates
can often be cumbersome
and confusing. To be more
precise, observations and
events are often recorded by
their Julian Date. The Julian
period was the brain-
child of the 16th
century historianJoseph Justus Scaliger and
begins on Jan. 1, 4713 b.c.
This date is one where several
cycles coincide: the 28-year
solar cycle in the Julian calen-
dar, after which the days of
the year fall on the same days
of the week; the 19-year
Metonic cycle, when lunar
phases recur on the same days
of the year; and the 15-year
indiction cycle, the tax cycle
of the Roman Empire, which
was another method for
recording dates.
When John Herscheladapted Scaliger’s idea
for astronomical use
in 1849, he chose
noon as the zero hour
for the current Julian
Period, thus avoiding
a date change during
nighttime observa-
tions. Julian Date
is then simply the
number of days that
have passed since
noon on Jan. 1,
4713 b.c.
In 1957, the
Smithsonian
Astrophysical
Observatory created a
Modified Julian Date,
which begins
at midnight GMT,
Nov. 17, 1858. This made the
day count considerably
smaller and more manage-
able for early computers.
Time and astronomy are
rooted in the way we order
our lives. Ancient sky watch-
ers looked to the sky to bring
order to their world, and we
still use astronomical cycles
to set the very patterns of our
lives. Astronomers have given
these patterns order and pre-
cision in an effort to answer
that age-old question: “What
time is it?”WWW.ASTRONOMY.COM 57
Raymond Shubinski is a contributing editor of Astronomy. He
loves winding his clocks and keeping time with the cosmos under
the clear skies of the Great Southwest.LEFT: Greenwich Observatory
stands on a hill overlooking the
River Thames, which allowed
nearby ships to set their clocks to
the time ball on its roof. Time balls
grew in popularity through the late
19th century and inspired the
annual New Year’s midnight ball
drop in New York City’s Times
Square. DAVID J. EICHERBELOW: In March 1911, English
newspapers took pleasure in
reporting that Gallic clocks were
being turned back to Greenwich
time, as evidenced by this
illustration in the Illustrated London
News. COURTESY RAYMOND SHUBINSKI